These numbers are “disastrously low”, according to Paul Mainwood, a Covid analyst, and only marginally better than Hong Kong – where roughly a third of those over 80 have had two jabs. In recent weeks the city has been battered by omicron, with hospitals and morgues overwhelmed. Around 90 per cent of deaths have been among the unvaccinated.

This contrasts to countries such as New Zealand and South Korea, where coverage is high among the most vulnerable. While both have seen unprecedented spikes in cases in the last six weeks as restrictions have finally eased, deaths have remained relatively low. 

In China, questions have also been raised about the quality of the vaccines used. The government has only approved shots developed and manufactured domestically, such as CoronaVac, Sinovac and Sinopharm.

Some early studies have signalled that these vaccines are less effective in the face of omicron. Last week, the analytics firm Airfinity said China is at more risk of a major omicron wave than Hong Kong “due to the lower efficacy [of] vaccines administered”.

Based on the case-fatality rate in the city, Airfinity estimated that up to one million people could die nationwide if China eased restrictions (or lost control of Covid) without first using Western vaccines in a widespread booster campaign.

Others, though, downplay these fears – arguing the vaccines themselves are less problematic than the take-up. They point to early analysis from Hong Kong, which suggests that although a third booster dose is critical, Sinovac is still holding up against severe disease and death.

“What really matters if zero Covid is breached is protection rates against severe disease and death,” said Mr Mainwood. “We’ve seen from the Hong Kong data that Chinese vaccines appear very close to the best mRNA vaccines [Pfizer and Moderna] on those measures.

“Chinese vaccines vary a lot more on their success in preventing symptomatic cases, but since no type [of vaccine] at all seems to be up to stopping a BA.2 [omicron] wave, this isn’t terribly important.”

But, in the short term at least, experts say China is unlikely to move away from stringent curbs to stamp out Covid. 

“The occurrence of outbreaks in a “Dynamic Zero Covid” strategy is inevitable, and there is a plan for outbreak response to ensure the number of infections is kept at a low level,” said Prof Ben Cowling, chair of epidemiology at the University of Hong Kong. “I would not expect any change to the strategy in the short term.

“I also think it’s unlikely that an outbreak of the scale of Hong Kong  – more than 60 per cent of population infected within three months – could occur in mainland China, because more stringent interventions are available to stop transmission.” 

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